title: Comparison of characteristics of natural autoantibodies against myeloperoxidase and anti-myeloperoxidase autoantibodies from patients with microscopic polyangiitis.
abstract: OBJECTIVE
  Natural autoantibodies (NAAs) against MPO exist in normal human plasma. In the current study, the immune characteristics of MPO-NAA and MPO-ANCA were examined and compared with the aim to investigate the pathogenesis of MPO-ANCA.
  
  
  METHODS
  MPO-NAAs were affinity purified from normal plasma of five healthy blood donors and one batch of IVIG. MPO-ANCAs were purified from plasma of 10 patients with MPA. Antigen specificity of the antibodies was tested by western blot analysis. The titre, the avidity, the Immunoglobulin G (IgG) subclasses and the effect of the antibodies towards the binding between ceruloplasmin and MPO were tested using ELISAs. The MPO-NAA-induced production of reactive oxygen species was assessed using oxidation of dihydrorhodamine (DHR) to rhodamine.
  
  
  RESULTS
  MPO-NAA recognized epitope(s) in the heavy chains of MPO with conformation-dependent structure, the same as MPO-ANCA. The median titre of MPO-NAA was lower than that of MPO-ANCA (1 : 40 vs 1 : 4800, P < 0.001). The median avidity of MPO-NAA was lower than that of MPO-ANCA (2.2 × 10(7) vs 8.7 × 10(7)/M, P = 0.014). The IgG subclasses of MPO-NAA were mainly restricted to IgG1 (100%) and lack of IgG3. The inhibition effect on the binding between ceruloplasmin and MPO was lower for MPO-NAA than MPO-ANCA (P = 0.046). The MPO-NAA-induced respiratory burst of neutrophils was significantly weaker than that of MPO-ANCA (P = 0.036).
  
  
  CONCLUSIONS
  The lower titre, lower avidity and lack of IgG3 subclass compared with MPO-ANCA may contribute to the non-pathogenic co-existence of MPO-NAA with MPO in serum.
authors.affiliation: Department of Medicine, Renal Division, Peking University First Hospital, Institute of Nephrology, Peking University, Key Laboratory of Renal Disease, Ministry of Health of China, Beijing, China.
authors.forename: Peng-Cheng
authors.initials: PC
authors.lastname: Xu
authors.forename: Zhao
authors.initials: Z
authors.lastname: Cui
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Thomas
authors.initials: T
authors.lastname: Hellmark
authors.forename: Ming-Hui
authors.initials: MH
authors.lastname: Zhao
mesh_terms: D000704:Analysis of Variance; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000276:immunology* / Q000378:metabolism; D001323:Autoantibodies / Q000276:immunology / Q000378:metabolism; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology* / Q000378:metabolism; D008297:Male; D055953:Microscopic Polyangiitis / Q000097:blood / Q000276:immunology* / Q000503:physiopathology; D009504:Neutrophils / Q000276:immunology / Q000378:metabolism; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D012016:Reference Values; D012494:Sampling Studies
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D001323:Autoantibodies; D007074:Immunoglobulin G; D009195:Peroxidase